JP2007188776A - Nonaqueous electrolytic solution battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution battery which suppresses mechanical property deterioration in a separator, and especially suppresses deterioration in high temperature storage, when the voltage of an open circuit ranges from 4.25 V to 4.60 V with a pair of fully charged positive and negative electrodes. <P>SOLUTION: This battery has an electrode 20 on which striped positive electrode 2 and negative electrode 3 have been wound via a separator 4 within the inside of a battery can 1. The separator 4 has an oxidant inhibitor which prevents the separator 4 from deteriorating due to oxidization. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte battery, and more particularly, to a nonaqueous electrolyte battery including a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator.

  Due to the remarkable development of portable electronic technology in recent years, mobile phones and notebook computers are recognized as basic technologies that support an advanced information society. Research and development related to the enhancement of the functions of these devices has been energetically advanced, and it has been an issue that the increase in power consumption due to the enhancement of functions shortens the driving time.

  In order to ensure a driving time of a certain level or higher, it is essential to increase the energy density of a secondary battery used as a driving power source. For example, a high-functional secondary battery represented by a lithium ion secondary battery or the like Further increase in energy density is expected.

  In a conventional lithium ion secondary battery, a lithium cobaltate is used for the positive electrode and a carbon material is used for the negative electrode, and the operating voltage has been used in the range of 4.2V to 2.5V. In the unit cell, the terminal voltage can be increased to 4.2 V largely due to excellent electrochemical stability of a non-aqueous electrolyte material or a separator.

  By the way, the positive electrode active material such as lithium cobaltate used in the conventional lithium ion secondary battery operating at a maximum of 4.2 V only uses a capacity of about 60% of its theoretical capacity. In principle, it is possible to utilize the remaining capacity by increasing the charging voltage. In fact, for example, as disclosed in Patent Document 1, it is known that high energy density is manifested by setting the voltage during charging to 4.25 V or more.

International Publication No. WO03 / 019713A1 Pamphlet

  However, under a high voltage of 4.25 V or more, the oxidizing atmosphere is strengthened particularly in the vicinity of the positive electrode, and the battery constituent material is easily oxidized. In particular, since the separator is made of polyolefin as a main raw material, it is susceptible to oxidative decomposition in a highly oxidative atmosphere, which causes a decrease in molecular weight due to oxidative decomposition and induces a significant decrease in mechanical properties, resulting in film breakage. In particular, the deterioration is remarkable under a high temperature atmosphere, and a short circuit occurs due to the film breakage, causing a significant decrease in battery characteristics.

  Therefore, an object of the present invention is to provide a separator for a non-aqueous electrolyte battery having an open circuit voltage of 4.25 V to 4.60 V in a fully charged state (hereinafter, appropriately referred to as a fully charged state) per pair of positive and negative electrodes. An object of the present invention is to provide a nonaqueous electrolyte battery that suppresses deterioration of mechanical properties, suppresses deterioration particularly when stored at high temperature, and suppresses deterioration of battery characteristics.

  The inventors of the present invention have found that the polyolefin microporous membrane used in the non-aqueous electrolyte battery is physically different from the positive electrode when the charging voltage is set to 4.25 V or more, particularly in the vicinity of the positive electrode surface. There are inherent problems with this battery system such that non-aqueous electrolyte materials and separators that come into contact are more susceptible to oxidative decomposition, resulting in increased internal resistance of the battery and deterioration of battery characteristics, especially at high temperatures. I found out.

That is, in order to solve the above-described problem, the present invention
The positive electrode and the negative electrode are arranged to face each other with a separator interposed therebetween,
In a non-aqueous electrolyte battery having an open circuit voltage of 4.25 V to 4.60 V in a fully charged state per pair of positive electrode and negative electrode,
The separator is a non-aqueous electrolyte battery having an antioxidant.

  In this invention, since the separator has an antioxidant, even if the open circuit voltage in a fully charged state is 4.25 V to 4.60 V in a high oxidation atmosphere under a high charging voltage, the raw material constituting the separator is oxidized. Suppresses deterioration. Thereby, it is possible to suppress deterioration of the battery characteristics particularly under high temperature storage.

  According to the present invention, in a non-aqueous electrolyte battery having an open circuit voltage of 4.25 V to 4.60 V in a fully charged state, the raw materials constituting the separator are suppressed from being deteriorated by oxidation, and thereby, particularly at high temperatures. Deterioration of battery characteristics under storage can be suppressed.

(1) First Embodiment (1-1) Configuration of Nonaqueous Electrolyte Battery Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a cross-sectional structure of a secondary battery using a microporous membrane according to the first embodiment of the present invention.

  In this secondary battery, the open circuit voltage in the fully charged state is, for example, 4.25V to 4.60V, 4.25 to 6.00V. This secondary battery is a so-called cylindrical type, and is a wound electrode in which a strip-shaped positive electrode 2 and a strip-shaped negative electrode 3 are wound via a separator 4 inside a substantially hollow cylindrical battery can 1. It has a body 20.

  The battery can 1 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 1, a pair of insulating plates 5 and 6 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 1, a battery lid 7, a safety valve mechanism 8 and a thermal resistance element (PTC element) 9 provided inside the battery lid 7 are interposed via a gasket 10. It is attached by caulking and the inside of the battery can 1 is sealed. The battery lid 7 is made of, for example, the same material as the battery can 1. The safety valve mechanism 8 is electrically connected to the battery lid 7 via a heat sensitive resistance element 9, and the disk plate 11 is reversed when the internal pressure of the battery becomes a certain level or more due to internal short circuit or external heating. Thus, the electrical connection between the battery lid 7 and the wound electrode body 20 is cut off. The heat-sensitive resistor element 9 limits the current by increasing the resistance value when the temperature rises, and prevents abnormal heat generation due to a large current. The gasket 10 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around, for example, the center pin 12. A positive electrode lead 13 made of aluminum or the like is connected to the positive electrode 2 of the wound electrode body 20, and a negative electrode lead 14 made of nickel or the like is connected to the negative electrode 3. The positive electrode lead 13 is welded to the safety valve mechanism 8 to be electrically connected to the battery lid 7, and the negative electrode lead 14 is welded to and electrically connected to the battery can 1.

[Positive electrode]
FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. As shown in FIG. 2, the positive electrode 2 includes, for example, a positive electrode current collector 2A having a pair of opposed surfaces, and a positive electrode mixture layer 2B provided on both surfaces of the positive electrode current collector 2A. In addition, you may make it have the area | region where the positive mix layer 2B was provided only in the single side | surface of 2 A of positive electrode collectors. The positive electrode current collector 2A is made of, for example, a metal foil such as an aluminum (Al) foil. The positive electrode mixture layer 2B includes, for example, a positive electrode active material, and may include a conductive agent such as graphite and a binder such as polyvinylidene fluoride as necessary.

As the positive electrode active material, a lithium-containing compound, for example, lithium oxide, lithium sulfide, or an intercalation compound containing lithium is suitable, and two or more of these may be mixed and used. In particular, in order to increase the energy density, it is preferable to include a lithium composite oxide mainly composed of Li _x MO ₂ as a positive electrode active material. M is preferably one or more transition metals, specifically, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), aluminum (Al), vanadium (V) and titanium ( At least one of the group consisting of Ti) is preferred. In addition, x varies depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such lithium composite oxide include, for example, Li _a CoO ₂ (a≈1), Li _b NiO ₂ (b≈1), or Li _c Ni _d Co _1-d O ₂ (c≈1, 0 <d <1). Examples of the lithium composite oxide include Li _e Mn ₂ O ₄ (e≈1) having a spinel structure or Li _f FePO ₄ (f≈1) having an olivine structure.

  More specifically, a lithium transition metal composite oxide having a composition represented by (Chemical Formula 1) to (Chemical Formula 5) described below can be used.

(Chemical formula 1)
_{Li [Li x Mn (1-} xyz) Ni y M 'z] O (2-a) F b
(Wherein M ′ is cobalt (Co), manganese (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu ), Zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), and x represents at least one element. 0 <x ≦ 0.2, y is 0.3 ≦ y ≦ 0.8, z is 0 ≦ z ≦ 0.5, a is −0.1 ≦ a ≦ 0.2, b is 0 ≦ b ≦ 0 A value within the range of .1.)

(Chemical formula 2)
Li _c Ni _(1-d) M '' _d O _(2-e) F _f
(Where M ″ is cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron ( It represents at least one element selected from Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). Is -0.1≤c≤0.1, d is 0.005≤d≤0.5, e is -0.1≤e≤0.2, and f is in the range of 0≤f≤0.1. Value.)

(Chemical formula 3)
Li _c Co _(1-d) M ''' _d O _(2-e) F _f
(Where M ′ ″ is nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron It represents at least one element selected from (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). c is −0.1 ≦ c ≦ 0.1, d is 0 ≦ d ≦ 0.5, e is −0.1 ≦ e ≦ 0.2, and f is a value within the range of 0 ≦ f ≦ 0.1. .)

(Chemical formula 4)
Li _s Mn _2-t M '''' _t O _u F _v
(Where M ″ ″ is cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), Represents at least one element selected from iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W) S is a value within a range of s ≧ 0.9, t is 0.005 ≦ t ≦ 0.6, u is 3.7 ≦ u ≦ 4.1, and v is a value within a range of 0 ≦ v ≦ 0.1. )

  Moreover, the lithium transition metal composite phosphate which has a composition represented by (Formula 5) described below can also be used.

(Chemical formula 5)
LiM '''''PO ₄
(Where M ′ ″ ″ is cobalt (Co), manganese (Mn), iron (Fe), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti). , Vanadium (V), niobium (Nb), copper (Cu), zinc (Zn), molybdenum (Mo), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr) Represents one or more elements.)

[Negative electrode]
As shown in FIG. 2, the negative electrode 3 includes, for example, a negative electrode current collector 3A having a pair of opposed surfaces, and a negative electrode mixture layer 3B provided on both surfaces of the negative electrode current collector 3A. In addition, you may make it have the area | region in which the negative mix layer 3B was provided only in the single side | surface of 3 A of negative electrode collectors. The negative electrode current collector 3A is made of a metal foil such as a copper (Cu) foil. The negative electrode mixture layer 3B includes, for example, a negative electrode active material, and may include a binder such as polyvinylidene fluoride as necessary.

The negative electrode active material includes a negative electrode material capable of inserting and extracting lithium (hereinafter, appropriately referred to as a negative electrode material capable of inserting and extracting lithium). Examples of negative electrode materials capable of inserting and extracting lithium include carbon materials, metal compounds, oxides, sulfides, lithium nitrides such as LiN ₃ , lithium metals, metals that form alloys with lithium, or polymer materials. Is mentioned.

  Examples of the carbon material include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compound fired bodies, carbon fibers, and activated carbon. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and part of it is non-graphitizable carbon or graphitizable carbon. Some are classified as: Examples of the polymer material include polyacetylene and polypyrrole.

  Among such negative electrode materials capable of inserting and extracting lithium, those having a charge / discharge potential relatively close to lithium metal are preferable. This is because the lower the charge / discharge potential of the negative electrode 3, the easier the battery has a higher energy density. Among these, a carbon material is preferable because a change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Moreover, non-graphitizable carbon is preferable because excellent cycle characteristics can be obtained.

  Examples of the negative electrode material capable of inserting and extracting lithium include lithium metal alone, a metal element or a metalloid element capable of forming an alloy with lithium, an alloy, or a compound. These are preferable because a high energy density can be obtained, and in particular, when used together with a carbon material, a high energy density can be obtained and excellent cycle characteristics can be obtained, and therefore, it is more preferable. Note that in this specification, alloys include those composed of one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. The structures include solid solutions, eutectics (eutectic mixtures), intermetallic compounds, or those in which two or more of them coexist.

Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), and cadmium. (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf). It is done. These alloys or compounds, for example, those represented by the chemical formula Ma _s Mb _t Li _u or a chemical formula Ma _p Mc _q Md _r,. In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of a metal element and a metalloid element other than lithium and Ma, Mc represents at least one of nonmetallic elements, and Md represents at least one of metallic elements and metalloid elements other than Ma. The values of s, t, u, p, q, and r are s> 0, t ≧ 0, u ≧ 0, p> 0, q> 0, and r ≧ 0, respectively.

  Among these, a simple substance, alloy or compound of a group 4B metal element or metalloid element in the short-period type periodic table is preferable, and silicon or tin, or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.

In addition, inorganic compounds that do not contain lithium, such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS, can also be used for either the positive or negative electrode.

[Electrolyte]
As the electrolytic solution, a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent can be used. As the non-aqueous solvent, for example, it is preferable to contain at least one of ethylene carbonate and propylene carbonate. This is because the cycle characteristics can be improved. In particular, it is preferable to mix and contain ethylene carbonate and propylene carbonate because cycle characteristics can be further improved. The nonaqueous solvent preferably contains at least one of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, or methyl propyl carbonate. This is because the cycle characteristics can be further improved.

  The non-aqueous solvent preferably further contains at least one of 2,4-difluoroanisole and vinylene carbonate. This is because 2,4-difluoroanisole can improve discharge capacity, and vinylene carbonate can further improve cycle characteristics. In particular, it is more preferable that they are mixed and contained because both the discharge capacity and the cycle characteristics can be improved.

  Non-aqueous solvents further include butylene carbonate, γ-butyrolactone, γ-valerolactone, those in which part or all of the hydrogen groups of these compounds are substituted with fluorine groups, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl Tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide or trimethyl phosphate may be included. Yes.

  Depending on the electrode to be combined, the reversibility of the electrode reaction may be improved by using a material in which part or all of the hydrogen atoms of the substance contained in the non-aqueous solvent group are substituted with fluorine atoms. Therefore, these substances can be used as appropriate.

Examples of the lithium salt that is an electrolyte salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) _2. , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBF ₂ (ox), LiBOB, or LiBr are suitable, and one or more of these are used in combination. be able to. Among them, LiPF ₆ is preferable because it can obtain high ion conductivity and can improve cycle characteristics.

[Separator]
As a separator material, it is possible to use those used in conventional batteries. Among these, it is particularly preferable to use a polyolefin microporous film that is excellent in short-circuit prevention effect and that can improve battery safety by a shutdown effect. For example, a microporous film made of polyethylene or polypropylene resin is preferable.

  The separator 4 carries an antioxidant. Specifically, for example, a separator 4 previously coated with an antioxidant can be used. Moreover, what knead | mixed antioxidant beforehand in the raw material of the separator 4 can be used.

  By carrying an antioxidant on the separator 4, chain decomposition reaction due to radicals can be suppressed, and deterioration of the separator 4 can be suppressed. That is, the oxidative degradation of polyolefin is caused by the generation of radicals due to the extraction of hydrogen in the main chain, and the molecular chain of the polyolefin is successively decomposed by a chain reaction, causing a decrease in molecular weight. Polyolefins having a reduced molecular weight show a significant decrease in mechanical properties, become brittle and easily break. In order to suppress such a chain decomposition reaction due to radicals, an antioxidant is supported on the separator 4.

  As a method of applying the antioxidant to the surface of the separator 4, for example, a solution obtained by dissolving an antioxidant in an organic solvent is applied by a method such as dipping or spraying, and then the organic solvent is volatilized. Only the antioxidant can be provided on the separator 4. In addition, as a method of kneading the antioxidant into the separator 4, the antioxidant can be supported on the separator 4 by adding an antioxidant in advance to the raw material at the time of forming the separator.

  Since it is desirable that the antioxidant supported on the separator 4 be selectively present in the surface layer portion of the separator, it is preferable that the antioxidant does not dissolve in the electrolytic solution. However, it only needs to be present between the interface between the separator 4 and the electrode. It does not matter.

  In addition, it is desirable that the antioxidant is selectively present in the vicinity of the positive electrode because it is placed on the positive electrode side of the separator 4 that is placed in a strong oxidizing atmosphere. It is more effective to apply.

  Antioxidants do not depend on the type of antioxidant as long as they have a radical scavenger effect that deactivates the generated radicals and a peroxide effect that decomposes peroxides generated by the generated radicals. . For example, a phenolic antioxidant, a phosphorus antioxidant, and a sulfur antioxidant can be used.

  More specifically, examples of the phenolic antioxidant include tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, 1,3,5-trimethyl- 2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene or the like can be used. As the phosphorus-based antioxidant, for example, tris (2,4-di-t-butylphenyl) phosphite can be used. As the sulfur-based antioxidant, for example, dilauryl thiodipropionate, distearyl thiodipropionate and the like can be used.

  These antioxidants may be used alone, but more preferably used simultaneously. This is because a high synergistic effect is exhibited.

  The amount of the antioxidant added to the separator 4 is preferably 0.05 wt% or more and 5 wt% or less. This is because the antioxidant effect is weak when the addition amount of the antioxidant is less than 0.05 wt%. This is because if the added amount of the antioxidant is more than 5 wt%, the battery characteristics, particularly the initial charge / discharge efficiency, will be reduced.

  The presence of the antioxidant in the separator 4 can be confirmed by, for example, extracting the antioxidant from the separator 4 with a solvent and quantifying it with, for example, GC mass, liquid chromatography, or the like.

(1-2) Nonaqueous Electrolyte Battery Manufacturing Method Next, a nonaqueous electrolyte battery manufacturing method according to the first embodiment of the present invention will be described. Hereinafter, a nonaqueous electrolyte battery manufacturing method will be described by taking a cylindrical nonaqueous electrolyte battery as an example.

  The positive electrode 2 is produced as described below. First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a positive electrode mixture. Use slurry.

  Next, after applying this positive electrode mixture slurry to the positive electrode current collector 2A and drying the solvent, the positive electrode mixture layer 2B is formed by compression molding with a roll press or the like, and the positive electrode 2 is produced.

  The negative electrode 3 is produced as described below. First, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry.

  Next, after applying this negative electrode mixture slurry to the negative electrode current collector 3A and drying the solvent, the negative electrode mixture layer 3B is formed by compression molding using a roll press or the like, and the negative electrode 3 is produced.

  Next, the positive electrode lead 13 is attached to the positive electrode current collector 2A by welding or the like, and the negative electrode lead 14 is attached to the negative electrode current collector 3A by welding or the like. Next, the positive electrode 2 and the negative electrode 3 are wound through a separator 4 on which an antioxidant is previously supported, and the tip of the positive electrode lead 13 is welded to the safety valve mechanism 8 and the tip of the negative electrode lead 14 is connected to the battery. The positive electrode 2 and the negative electrode 3 which are welded to the can 1 and wound are sandwiched between a pair of insulating plates 5 and 6 and stored inside the battery can 1.

  Next, an electrolytic solution is injected into the battery can 1 and the separator 4 is impregnated with the electrolytic solution. Next, the battery lid 7, the safety valve mechanism 8, and the heat sensitive resistance element 9 are fixed to the opening end of the battery can 1 by caulking through the gasket 10. As described above, the nonaqueous electrolyte battery according to the first embodiment of the present invention is manufactured.

  In the nonaqueous electrolyte battery according to the first embodiment of the present invention, when charged, for example, lithium ions are released from the positive electrode 2 and inserted in the negative electrode 3 through the electrolytic solution. When discharging is performed, for example, lithium ions are detached from the negative electrode 3 and inserted into the positive electrode 2 through the electrolytic solution. In the first embodiment, since the antioxidant is supported on the separator 4 and the oxidation resistance is improved, the deterioration of the self-discharge rate especially during high temperature storage is suppressed, and high reliability is ensured.

(2) Second Embodiment (2-1) Configuration of Nonaqueous Electrolyte Battery FIG. 3 shows the structure of a nonaqueous electrolyte battery according to the second embodiment of the present invention. As shown in FIG. 3, the nonaqueous electrolyte battery is sealed by housing the battery element 30 in an exterior material 37 made of a moisture-proof laminate film and welding the periphery of the battery element 30. The battery element 30 is provided with a positive electrode lead 32 and a negative electrode lead 33, and these leads are sandwiched between outer packaging materials 37 and pulled out to the outside. A resin piece 34 and a resin piece 35 are coated on both surfaces of the positive electrode lead 32 and the negative electrode lead 33 in order to improve the adhesion to the exterior material 37.

[Exterior material]
The packaging material 37 has, for example, a stacked structure in which an adhesive layer, a metal layer, and a surface protective layer are sequentially stacked. The adhesive layer is made of a polymer film. Examples of the material constituting the polymer film include polypropylene (PP), polyethylene (PE), unstretched polypropylene (CPP), linear low density polyethylene (LLDPE), and low density. A polyethylene (LDPE) is mentioned. The metal layer is made of a metal foil, and an example of a material constituting the metal foil is aluminum (Al). Moreover, it is also possible to use metals other than aluminum as a material which comprises metal foil. Examples of the material constituting the surface protective layer include nylon (Ny) and polyethylene terephthalate (PET). The surface on the adhesive layer side is a storage surface on the side where the battery element 30 is stored.

[Battery element]
For example, as shown in FIG. 4, the battery element 30 includes a strip-shaped negative electrode 43 provided with a gel electrolyte layer 45 on both sides, a separator 44, and a strip-shaped positive electrode 42 provided with a gel electrolyte layer 45 on both sides. The battery element 30 is a wound type battery element 30 that is formed by laminating the separator 44 and wound in the longitudinal direction.

  The positive electrode 42 includes a strip-like positive electrode current collector 42A and a positive electrode active material layer 42B formed on both surfaces of the positive electrode current collector 42A. The positive electrode current collector 42A is a metal foil made of, for example, aluminum (Al).

  One end of the positive electrode 42 in the longitudinal direction is provided with a positive electrode lead 32 connected by, for example, spot welding or ultrasonic welding. As a material of the positive electrode lead 32, for example, a metal such as aluminum can be used.

  The negative electrode 43 includes a strip-shaped negative electrode current collector 43A and a negative electrode active material layer 43B formed on both surfaces of the negative electrode current collector 43A. The negative electrode current collector 43A is made of, for example, a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil.

  Similarly to the positive electrode 42, the negative electrode lead 33 connected by, for example, spot welding or ultrasonic welding is also provided at one end portion of the negative electrode 43 in the longitudinal direction. As a material of the negative electrode lead 33, for example, copper (Cu), nickel (Ni) or the like can be used.

  Since things other than the gel electrolyte layer 45 are the same as those in the first embodiment, the gel electrolyte layer 45 will be described below.

  The gel electrolyte layer 45 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 45 is preferable because it can obtain high ionic conductivity and prevent battery leakage. The configuration of the electrolytic solution (that is, the liquid solvent, the electrolyte salt, and the additive) is the same as that in the first embodiment.

  Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, from the viewpoint of electrochemical stability, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable.

(2-2) Method for Manufacturing Nonaqueous Electrolyte Battery Next, a method for manufacturing a nonaqueous electrolyte battery according to the second embodiment of the present invention will be described. First, a precursor solution containing a solvent, an electrolyte salt, a polymer compound, and a mixed solvent is applied to each of the positive electrode 42 and the negative electrode 43, and the mixed solvent is volatilized to form the gel electrolyte layer 45. In addition, the positive electrode lead 32 is attached to the end of the positive electrode current collector 42A in advance by welding, and the negative electrode lead 33 is attached to the end of the negative electrode current collector 43A by welding.

  Next, the positive electrode 42 and the negative electrode 43 formed with the gel electrolyte layer 45 are laminated in advance through a separator 44 on which an antioxidant is supported, and then the laminated body is wound in the longitudinal direction. A wound battery element 30 is formed.

  Next, a recess 36 is formed by deep drawing the exterior material 37 made of a laminate film, the battery element 30 is inserted into the recess 36, and an unprocessed portion of the exterior material 37 is folded back to the upper portion of the recess 36. The outer peripheral part of is thermally welded and sealed. As described above, the nonaqueous electrolyte battery according to the second embodiment of the present invention is manufactured.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited only to these examples.

  Table 1 shows the charging voltage, antioxidant, electrolyte form, addition amount, addition form, and remaining maintenance rate of the secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 11. Hereinafter, Examples 1 to 13 and Comparative Examples 1 to 11 will be described with reference to Table 1.

<Example 1>
The positive electrode 2 was produced as follows. First, a positive electrode active material was mixed with 98 wt% lithium cobaltate, 0.8 wt% amorphous carbon powder (Ketjen Black) as a conductive agent, and 1.2 wt% polyvinylidene fluoride as a binder. A mixture was prepared.

  Next, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode mixture slurry, and then this positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector made of a strip-shaped aluminum foil. . Next, after drying the obtained coating material with hot air, it was compression molded with a roll press to form a positive electrode mixture layer. Next, a positive electrode lead made of aluminum was welded.

  The negative electrode was produced as follows. First, 90 wt% of spherical graphite powder and 10 wt% of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Next, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to obtain a negative electrode mixture slurry. Next, this negative electrode mixture slurry was uniformly applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil, dried, and further compression-molded with a roll press to form a negative electrode mixture layer.

  Next, a separator having an antioxidant layer was prepared as described below. First, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, which is a hindered phenol-based antioxidant, and acetone are mixed at a mass ratio of 1:99, An antioxidant 1 wt% solution was prepared.

  Next, a PE microporous film having a thickness of 9 μm was immersed in this antioxidant solution, and then dried to obtain a separator having an antioxidant layer on the surface of the PE substrate. At this time, the antioxidant was 1.5 wt% with respect to the separator.

Next, after producing a positive electrode and a negative electrode, an aluminum positive electrode lead was attached to one end of the positive electrode current collector, and a nickel negative electrode lead was attached to one end of the negative electrode current collector. Next, a gel electrolyte layer was provided on the positive electrode mixture layer and the negative electrode mixture layer. As this gel electrolyte, a polyvinylidene fluoride as a matrix polymer and a hexafluoropropylene copolymer in which an electrolytic solution is held was used. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a content of 0.8 mol / kg in a solvent obtained by mixing 60 wt% of ethylene carbonate as a nonaqueous solvent and 40 wt% of propylene carbonate was used. .

  Next, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order, and a battery element was produced by winding this in a spiral shape. Next, the battery element was sealed under reduced pressure in an exterior material made of a laminate film while the positive electrode lead and the negative electrode lead were led out to the outside. Thus, the secondary battery of Example 1 was produced.

Measurement of Capacity Maintenance Rate (Remaining Maintenance Rate) In Example 1, charging was performed such that the open circuit voltage in a fully charged state was 4.35 V, and the fully charged secondary battery was placed in a constant temperature bath at 60 ° C. 20 A high-temperature storage test was conducted by allowing it to stand for days. Charging is performed at 23 ° C. until the battery voltage reaches 4.35 V at a current value that can discharge the theoretical capacity in 2 hours, and then at a constant voltage of 4.35 V for 5 hours. And fully charged.

Thereafter, discharging was performed at a constant current capable of discharging the theoretical capacity in 2 hours until the battery voltage reached 3.0 V, and the discharge capacity at this time was defined as the remaining capacity. Moreover, about the fully charged secondary battery before a high temperature storage test, it discharged on the same conditions, and let the discharge capacity at this time be a full charge capacity. Next, the capacity retention rate after the high-temperature storage test was calculated from the remaining capacity and the full charge capacity according to the following formula 1.
(Formula 1)
(Capacity maintenance ratio) = (Remaining capacity / Full charge capacity) × 100 (%)

<Example 2 to Example 8>
<Example 2>
A secondary battery of Example 2 was produced in the same manner as Example 1. Charging was performed such that the open circuit voltage in the fully charged state was 4.25V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 3>
A secondary battery of Example 3 was fabricated in the same manner as Example 1. Charging was performed such that the open circuit voltage in the fully charged state was 4.30V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 4>
A secondary battery of Example 4 was produced in the same manner as Example 1. Charging was performed so that the open circuit voltage in the fully charged state was 4.40V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 5>
A secondary battery of Example 5 was fabricated in the same manner as Example 1. Charging was performed so that the open circuit voltage in the fully charged state was 4.45V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 6>
A secondary battery of Example 6 was made in the same manner as Example 1. Charging was performed such that the open circuit voltage in the fully charged state was 4.50V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 7>
A secondary battery of Example 7 was produced in the same manner as Example 1. Charging was performed so that the open circuit voltage in a fully charged state was 4.55V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 8>
A secondary battery of Example 8 was made in the same manner as Example 1. Charging was performed so that the open circuit voltage in the fully charged state was 4.60V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 9>
A secondary battery of Example 9 was produced in the same manner as in Example 1 except that tris (2,4-di-t-butylphenyl) phosphite, which is a phosphorus-based antioxidant, was used as the antioxidant. did. Charging was performed such that the open circuit voltage in the fully charged state was 4.35V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 10>
A secondary battery of Example 10 was made in the same manner as Example 1 except that dilauryl thiodipropionate, which is a sulfur-based antioxidant, was used as the antioxidant. Charging was performed so that the open circuit voltage in the fully charged state was 4.35V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

<Example 11>
A secondary battery of Example 11 was produced in the same manner as in Example 1 except that the antioxidant was kneaded into the separator as described below. Charging was performed such that the open circuit voltage in the fully charged state was 4.35V. Next, a high temperature storage test was performed in the same manner as in Example 1, and the capacity retention rate after the high temperature storage test was measured.

  First, a mixture of ultra high molecular weight polyethylene having a weight average molecular weight of 2 million and high density polyethylene having a weight average molecular weight of 700,000 and a liquid paraffin as a solvent mixed at a mass ratio of 30:70, Tris (2,4-di-t-butylphenyl) phosphite, an antioxidant, is added and mixed uniformly to form a slurry, which is dissolved and kneaded using a twin-screw kneader at a temperature of 180 ° C. did. The amount of tris (2,4-di-t-butylphenyl) phosphite added was 2.0 wt% with respect to polyethylene.

  Next, the kneaded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled to form a 5 mm sheet. The quenched sheet was heated and pressed at a temperature of 115 ° C., and biaxially stretched 3.5 × 3.5 times at 120 ° C. in the vertical and horizontal directions, and after solvent removal treatment using heptane, at 100 ° C. Heat treatment was performed for 5 minutes to obtain a PE microporous film.

<Example 12>
Tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane / tris (2,4-di-t-butylphenyl) phosphite = 2/1 as an antioxidant (Mass ratio) and acetone were mixed at a mass ratio of 1:99 to prepare a 1 wt% antioxidant solution. This antioxidant was 1.4 wt% with respect to the separator. A secondary battery of Example 12 was made in the same manner as Example 1 except for the above. Charging was performed such that the open circuit voltage in the fully charged state was 4.35V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Example 13>
The positive electrode and the negative electrode were produced in the same manner as in Example 1. The separator having the antioxidant layer was produced as described below.

  First, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane and acetone were mixed at a mass ratio of 2:98 to prepare a 2 wt% antioxidant solution. Next, a PE microporous film having a thickness of 20 μm was immersed in this solution in the same manner as in Example 1, and then dried. At this time, the antioxidant was 1.7 wt% with respect to the separator.

  The separator, the positive electrode, and the negative electrode were laminated in the order of the negative electrode, the separator, the positive electrode, and the separator, and wound many times in a spiral shape to produce a jelly roll type wound electrode body.

  After producing the wound electrode body, a pair of insulating plates are arranged perpendicularly to the peripheral surface of the wound electrode body so as to sandwich the wound electrode body, and in order to collect the positive electrode, it is made of aluminum. One end of the positive electrode lead was led out from the positive electrode current collector, and the other end was electrically connected to the battery lid via a disk plate. Further, in order to collect the negative electrode current, one end of a nickel negative electrode lead was led out from the negative electrode current collector, and the other end was welded to the battery can. In addition, the wound electrode body was housed in the battery can, and 4.0 g of the electrolyte solution was injected into the battery can by a reduced pressure method.

For the electrolytic solution, a mixed solvent in which 35 wt% of ethylene carbonate, 63 wt% of dimethyl carbonate and 2 wt% of vinylene carbonate were mixed was prepared. Further, a solution in which LiPF ₆ was dissolved in this mixed solvent so that the molar concentration was 1.5 mol / kg was used. Finally, the battery can was caulked through a gasket coated with asphalt, and the safety valve mechanism, the heat sensitive resistance element, and the battery lid were hermetically sealed. Thus, a cylindrical secondary battery of Example 13 was produced. Charging was performed such that the open circuit voltage in the fully charged state was 4.35V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 1>
A secondary battery of Comparative Example 1 was produced in the same manner as Example 1 except that the antioxidant was not applied. Charging was performed such that the open circuit voltage in the fully charged state was 4.35V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative example 2>
A secondary battery of Comparative Example 2 was fabricated in the same manner as Comparative Example 1. Charging was performed such that the open circuit voltage in the fully charged state was 4.25V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 3>
A secondary battery of Comparative Example 3 was produced in the same manner as Example 1. Charging was performed so that the open circuit voltage in a fully charged state was 4.2V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative example 4>
A secondary battery of Comparative Example 4 was fabricated in the same manner as Comparative Example 1. Charging was performed so that the open circuit voltage in a fully charged state was 4.2V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 5>
A secondary battery of Comparative Example 5 was produced in the same manner as Comparative Example 1. Charging was performed such that the open circuit voltage in the fully charged state was 4.3V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 6>
A secondary battery of Comparative Example 6 was fabricated in the same manner as Comparative Example 1. Charging was performed so that the open circuit voltage in the fully charged state was 4.4V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 7>
A secondary battery of Comparative Example 7 was fabricated in the same manner as Comparative Example 1. Charging was performed so that the open circuit voltage in the fully charged state was 4.45V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 8>
A secondary battery of Comparative Example 8 was produced in the same manner as Comparative Example 1. Charging was performed so that the open circuit voltage in a fully charged state was 4.5V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 9>
A secondary battery of Comparative Example 9 was produced in the same manner as Comparative Example 1. Charging was performed so that the open circuit voltage in a fully charged state was 4.55V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 10>
A secondary battery of Comparative Example 10 was fabricated in the same manner as Comparative Example 1. Charging was performed so that the open circuit voltage in a fully charged state was 4.6V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

<Comparative Example 11>
A secondary battery of Comparative Example 11 was made in the same manner as Example 13 except that the antioxidant was not applied. Charging was performed such that the open circuit voltage in the fully charged state was 4.35V. Next, in the same manner as in Example 1, a high temperature storage test was performed, and the capacity retention rate after the high temperature storage test was measured.

As shown in Evaluation Table 1, in Example 1, the capacity retention rate is 82%, and in Comparative Example 1, the capacity retention rate is 60%. Example 1 showed a better capacity retention rate than Comparative Example 1. In Example 2, the capacity maintenance rate is 88%, and in Comparative Example 2, the capacity maintenance rate is 60%. Example 2 showed a better capacity retention rate than Comparative Example 2.

  In Examples 3 to 8, a decrease in capacity retention rate is observed with an increase in charging voltage, but no antioxidant is contained, and both have higher capacity retention rates than those with the same charging voltage. Indicated.

  In Example 9, the capacity retention rate was 80%, which was a better capacity retention rate than Comparative Example 1. In Example 10, the capacity retention rate was 80%, which was a better capacity retention rate than Comparative Example 1. In Example 11, the capacity retention rate was 83%, which was a better capacity retention rate than Comparative Example 1. In Example 12, the capacity retention rate was 84%, which was a better capacity retention rate than Comparative Example 1. In Example 13, the capacity retention rate was 82%, which was a better capacity retention rate than Comparative Example 11.

  In Comparative Example 3 and Comparative Example 4, both showed a good capacity retention rate, and there was no difference between the case where the antioxidant was added and the case where the antioxidant was not added.

  The present invention is not limited to the above-described embodiments of the present invention, and various modifications and applications are possible without departing from the spirit of the present invention. For example, the shape is not particularly limited. It may be a cylindrical shape, a square shape, a coin shape, a button shape, or the like.

  In the first embodiment, the non-aqueous electrolyte battery having an electrolyte as an electrolyte has been described. In the second embodiment, the non-aqueous electrolyte battery having a gel electrolyte as an electrolyte has been described. However, the present invention is not limited thereto. is not.

  For example, as the electrolyte, in addition to the above-described ones, a polymer solid electrolyte using an ion conductive polymer or an inorganic solid electrolyte using an ion conductive inorganic material can be used. It may be used in combination with the electrolyte. Examples of the polymer compound that can be used for the polymer solid electrolyte include polyether, polyester, polyphosphazene, and polysiloxane. Examples of the inorganic solid electrolyte include ion conductive ceramics, ion conductive crystals, and ion conductive glass.

It is a schematic sectional drawing of the nonaqueous electrolyte battery by 1st Embodiment of this invention. FIG. 2 is an enlarged sectional view of a part of a wound electrode body shown in FIG. 1. It is the schematic which shows the structure of the nonaqueous electrolyte battery by 2nd Embodiment of this invention. FIG. 4 is an enlarged cross-sectional view of a part of the battery element shown in FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery can 2 ... Positive electrode 2A ... Positive electrode collector 2B ... Positive electrode mixture layer 3A ... Negative electrode collector 3B ... Negative electrode mixture layer 3 ... Negative electrode 4. .. Separator 5, 6 ... Insulating plate 7 ... Battery cover 8 ... Safety valve mechanism 9 ... Heat sensitive resistance element 10 ... Gasket 11 ... Disc plate 12 ... Center pin 13 .... Positive electrode lead 14 ... Negative electrode lead 20 ... Winding electrode body 30 ... Battery element 32 ... Positive electrode lead 33 ... Negative electrode lead 34, 35 ... Resin piece 35 ... Negative electrode lead 36 ... Recess 37 ... Exterior material 42 ... Positive electrode 42A ... Positive electrode current collector 42B ... Positive electrode mixture layer 43 ... Negative electrode 43A ... Negative electrode current collector 43B ... Negative electrode Mixture layer 44 ... Separator 45 ... Gel electrolyte layer

Claims (6)

The positive electrode and the negative electrode are arranged to face each other with a separator interposed therebetween,
In a non-aqueous electrolyte battery having an open circuit voltage of 4.25 V to 4.60 V in a fully charged state per pair of the positive electrode and the negative electrode,
The non-aqueous electrolyte battery, wherein the separator has an antioxidant. In claim 1,
The non-aqueous electrolyte battery, wherein the antioxidant is provided on the surface of the separator. In claim 1,
The non-aqueous electrolyte battery, wherein the antioxidant is contained in the separator. In claim 1,
The non-aqueous electrolyte battery, wherein the antioxidant is added in an amount of 0.05 wt% to 5 wt% with respect to the separator. In claim 1,
The non-aqueous electrolyte battery, wherein the antioxidant functions as a radical scavenger or a peroxide decomposer. In claim 1,
The non-aqueous electrolyte battery is characterized in that the antioxidant is at least one selected from the group consisting of a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant.

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